Just keep your total chlorine levels at 12-15 ppm and keep hitting it with chlorine morning, noon, and night until the FC starts to hold! It might take a LOT of bleach but it will eventually hold. If you let your chlorine levels yo-yo up and down it will take longer so just keep testing and adding bleach to keep the level at about 12-15 ppm and you should be fine.

For more info read the posts by PoolDoc (Ben) in this thresd
http://www.poolforum.com/pf2/showthread.php?t=401